Implants such as stents and occlusive coils have been used in patients for a wide variety of reasons. One of the most common “stenting” procedures is carried out in connection with the treatment of atherosclerosis, a disease which results in a narrowing and stenosis of body lumens, such as the coronary arteries. At the site of the narrowing (i.e., the site of a lesion) a balloon is typically dilated in an angioplasty procedure to open the vessel. A stent is then set in apposition to the interior surface of the lumen in order to help maintain an open passageway. This result may be effected by means of the stent scaffolding support alone, or by virtue of the presence of one or more drugs carried by the stent to aide in the prevention of restenosis.
Various stent designs have been developed and used clinically, but self-expandable and balloon-expandable stent systems and their related deployment techniques are now predominant. Examples of self-expandable stents currently in use are the Magic WALLSTENT® stents and Radius stents (Boston Scientific). A commonly used balloon-expandable stent is the Cypher® stent (Cordis Corporation). Additional self-expanding stent background is presented in: “An Overview of Superelastic Stent Design,” Min. Invas Ther & Allied Technol 2002: 9(3/4) 235-246, “A Survey of Stent Designs,” Min. Invas Ther & Allied Technol 2002: 11(4) 137-147, and “Coronary Artery Stents: Design and Biologic Considerations,” Cardiology Special Edition, 2003: 9(2) 9-14, “Clinical and Angiographic Efficacy of a Self-Expanding Stent” Am Heart J 2003: 145(5) 868-874.
A simple example of a self-expanding stent deployment system is described in U.S. Pat. No. 4,580,568 (Gianturco) in which a sheath restraining a stent overrides a pusher rod or tube. The reference shows a stent resiliently compressed in shape for delivery in which straight sections of the stent are arranged side-by-side and closely adjacent one another. Stents are delivered by passing them through the sheath using the pusher. No reference is made regarding use of a guidewire.
Other examples of self-expanding stent deployment systems are presented in U.S. Pat. No. 4,830,003 (Wolff, et al.) and U.S. Pat. No. 5,064,435 (Porter). In each, an outer sheath overriding an inner tubular member restrains a stent until the sheath is withdrawn. The tubular member has a lumen adapted to receive a guidewire and a distal end adapted to abut the stent for delivery. In these patents, the figures clearly illustrate the stent open to such an extent that it clearly will not interfere with passing the device over the guidewire used to navigated to the treatment site.
The ability to advance these systems over a guidewire is advantageous for a number of reasons. For one, the guidewire is the optimal device for navigating to and crossing a lesion. Also, the wire remains in place at the desired treatment site while the delivery system is simply advanced over the wire to reach the treatment site. Furthermore, medical practitioners become accustomed to using one or more particular guidewires.
Foregoing these advantages in hopes of achieving others, some inventors have sought to combine delivery device and guidewire functionality. One such system is described in U.S. Pat. No. 6,280,465 (Cryer). The device described in connection with FIG. 4 of Cryer includes a coil stent set upon a central guidewire member, over which a tubular sheath and pusher are disposed. In use, the combination is advanced to a treatment site within a guiding catheter as an integral assembly. U.S. Patent Application Publication No. 2003/0163156 (Hebert, et al.) describes a system that is indistinguishable from Cryer except in that the guidewire core carrying the stent integrally includes one or more stent interface features instead of using a separate pusher.
While these systems might be suitable for some applications, they cannot offer “true” guidewire performance. The multiple overlapping layers of a “guidewire” core, sheath, pusher (sometimes) and stent are too bulky to rival the performance of a true guidewire in terms of flexibility, torquability, navigation ability, etc.
Another class of sheath-based stent delivery systems seeks advantage through including an integral balloon. One such system is presented in the above-referenced Hebert application as well as U.S. Pat. No. 5,019,090 (Pinchuck) and U.S. Pat. No. 6,071,286 (Mawad). In each example, a distal balloon and a self-expanding stent is set upon a balloon catheter body, with a proximal sheath holding the stent until withdrawn. A reverse approach is shown in U.S. Pat. No. 5,192,297 (Hull) in which a sheath covers both a proximal balloon and a distal self-expanding stent.
Another type of combined self-expanding stent/balloon device is described in U.S. Pat. No. 6,702,843 (Brown, et al.) and U.S. Pat. No. 5,843,090 (Schuetz). In each, a stent is set upon an inner tubular member and held in a compressed configuration by an outer catheter body that includes a balloon. The stent is stabilized by a blocker associated with the inner tubular member so that upon withdrawal of the outer body (including the balloon), the stent is released.
PCT Publication No. US2004/008909 to Nikolchev et al. discloses yet another type of combined self-expanding stent/balloon device. Here, a stent is set over upon a core wire including a blocker element and received within the lumen of a balloon catheter to releasably restrain the stent.
Of all the balloon-combination devices described above, only the commonly-assigned PCT application described a system that delivers the stent directly upon a core wire. Each of the others sets the stent upon a tubular body for receiving a guidewire, thus severely limiting system miniaturization.
Still, the overall use of the '909 system is handicapped just as the Cryer and Hebert simple-sheath systems described above; none of these devices integrating a guidewire or guidewire-like body for the core can match the performance of an off-the-shelf guidewire for navigating tortuous anatomy. Accordingly, a need persists for stent space-efficient delivery systems with which a practitioner may still use a favored guidewire for navigation to a treatment site.